A spool valve type solenoid valve is widely used, wherein a spool is slidably set up along an inner circumferential surface of a sleeve in which a port is formed on a side face thereof and a position of the spool is controlled by an electromagnetic force by solenoid and a mechanical force of a spring and the like; and the pressure of working fluid is controlled thereby. In this type of solenoid valves, it is necessary to provide clearance between the sleeve and the spool, so that it is difficult to completely prevent leakage between these two. As a method for reducing the leakage, the following solutions can be considered such that a length of a sliding portion is made longer, or such that clearance is made very small, which require highly accurate processing to result in growing processing cost.
As a solution showing good sealing characteristics for solving the above problem, for example, a solenoid valve, in which a poppet valve disclosed in Japanese Patent No 3994871 (Patent Document 1) and PCT International Publication No. WO2009/025366 (Patent Document 2) is used, is known.
A pressure proportional control valve disclosed in Japanese Patent No 3994871 has a first poppet valve mounted on a divider fixedly set up in a communication chamber formed between an input port and an output port and a second poppet valve arranged at a side opposite to an input port communicating side of the communication chamber communicating to the output port, wherein fluid pressure can be controlled proportionally with respect to output of the solenoid by making a seal sliding diameter of an inner circumference bore of the divider (a seal sliding diameter of a valve body of the first poppet valve, a first seal sliding diameter), a seating diameter of a valve portion of the first poppet valve and a seating diameter of the second poppet valve (abutting diameter) equally.
Also, a control valve disclosed in PCT International Publication No. WO2009/025366 has a structure, in which a valve portion of a first poppet valve and a valve portion of a second poppet valve are integrally formed as a valve portion body; this valve portion body is supported by a first pressure-sensing spring device constituted by bellows; and a valve seating body of the second poppet valve is supported by a second pressure-sensing spring device constituted by bellows, wherein a pressure receiving area of the first pressure-sensing spring device, a pressure receiving area of the second pressure-sensing spring device, a seating diameter of the valve portion of the first poppet valve and a seating diameter of the valve portion of the second poppet valve are made approximately equal to each other to result in good control characteristics.
[Patent Document 1] Japanese Patent No 3994871
[Patent Document 2] PCT International Publication No. WO2009/025366